Irons for clothing have a heated sole plate with which a user may smooth out unwanted clothing creases, and reinforce or create desired creases. Heating energy is usually provided by a thermostatically controlled electric element, and the temperature of the sole plate is typically selected by the user to suit the nature of the clothing to be ironed. The user may lightly damp the clothing, in order to better eliminate unwanted creases.
In a refinement an iron may be provided with a water tank, and a valve assembly whereby water can be admitted from the tank to outlets of the heated sole plate where it vaporises, and issues as steam. This arrangement avoids the need for damping of clothing and can give a superior and faster ironing action.
In one known arrangement a progressive slide valve is provided whereby water is continually passed through the sole plate to give a substantially constant steaming effect. The slide valve typically has a variable opening so as to permit the volume of stream to be selected. In another arrangement a manual pump is provided whereby the use may force some water through the sole plate to give a single burst of steam. Both of these arrangements are often provided in clothing irons.
One known problem of steam irons is the phenomenon of dripping, in which unvaporised water escapes from the sole plate onto the clothing. Such dripping is usually caused by an inappropriate relationship between the temperature of the sole plate and the volume of water admitted via the slide valve, so that there is insufficient heat capacity to vaporise all of the water passing through the soleplate. Dripping may also be caused by inevitable hysteresis exhibited by the sole plate thermostat, so that as the temperature of the sole plate falls to a minimum, some water droplets escape. At higher sole plate temperature, such droplets are vaporised.
In order to solve the dripping problem it has been proposed to incorporate a closure valve actuated by a bi-metallic control element in the water supply passage to the sole plate. As is well known, the degree of curvature of such a control element can change appreciably on heating, and can be used to move the closure valve so as to block and unblock water flow. Thus water flow may be inhibited below a predetermined minimum sole plate temperature, so that dripping is largely prevented.
However, the prior art solutions do not entirely solve the problem of dripping. Furthermore such bi-metallic control elements may exhibit an undesirable clicking sound during operation.
What is required is an improved means of relating water flow and hence potential steam generation, to sole plate temperature. The elimination of bi-metallic control elements would be advantageous in order to avoid unwanted hysteresis, and variability due to manufacturing and assembly inconsistences.